The sign is at the base of the April 25 Bridge. The bridge over the Tagus River, connecting Lisbon with the Alameda, is one of the longest suspension bridges in the world. At the time of its construction in 1966, the Salazar Bridge was named after the Prime Minister of Portugal, and after the Clove Revolution, in which Portugal switched to a democratic system of government, also called the April 25 Revolution, the name of the bridge was changed.
The bridge was photographed that day Click for a larger image Click for a larger image
In the next picture you can see the beginning of the bridge near the place of sign Click for a larger image
The base of the bridge and the sign on it can be seen in the next photo Click for a larger image